This invention relates to xerography and, more particularly, to an improved flash fusing method and apparatus for fixing toner images to copy substrates.
In the process of xerography, a light image of an original to be copied is typically recorded in the form of a latent electrostatic image upon a photosensitive member with subsequent rendering of the latent image visible by the application of electroscopic marking particles, commonly referred to as toner. The visual toner image can be either fixed directly upon the photosensitive member or transferred from the member to another support, such as a sheet of plain paper, with subsequent affixing of the image thereto in one of various ways, as for example by heat.
In order to affix or fuse electrostatic toner material onto a support member by heat alone, it is necessary to provide sufficient heat to raise the temperature of the toner material to a point at which the individual particles of the toner material become tacky and coalesce. This action causes the toner to flow to some extent into the fibers or pores of support members or otherwise upon the surfaces thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing it to be firmly bonded to the support member. In both the xerographic as well as the electrographic recording arts, the use of thermal energy for fixing toner images onto a support member, e.g., paper, is old and well known.
One approach to thermal fixing of toner images is to expose the toner image to a flash lamp of the xenon type. First attempts at flash fusing used a single flash of the xenon lamp to expose the entire image or copy sheet. As will be appreciated, a high voltage source is required to effect fusing of a typical 81/2.times.11 document with a single flash. Typically, the flash is effected by triggering a capacitor previously charged for such purposes. Thus, the power supply and storage capacitor required are very expensive and quite large.
Further developments in the area of flash fusing, in view of the foregoing, led to a flash fusing system designed to expose or couple only half of the image (i.e., half of a copy page) to a single flash resulting in the employment of two flashes to effect fusing of the entire image. Obviously, the energy required for each flash in this type of system is only one half of the total energy required to fuse the entire image with a single flash, thereby resulting in a lower cost and smaller power supply.
Recent efforts to further reduce the size and cost of flash fusing systems has resulted in a totally new and different approach to flash fusing.